Provide a page template for CSS data types

### MDN URL

https://developer.mozilla.org/en-US/docs/MDN/Writing_guidelines/Page_structures/Page_types#css_feature_reference_page

### What specific section or headline is this issue about?

_No response_

### What information was incorrect, unhelpful, or incomplete?

There's no page template for CSS data types, and the existing pages for data types are also quite disparate.

Specifically, it would be much better to have a guideline on the organization of the "Syntax", "Values", "Formal syntax", "Description", and "Interpolation" sections. (The "Description" section is rarely seen on pages for CSS properties, though.)

### What did you expect to see?

1. A template for CSS data types in the "CSS feature reference page" [section](https://developer.mozilla.org/en-US/docs/MDN/Writing_guidelines/Page_structures/Page_types#css_feature_reference_page) on the "Page type" page.
2. Accompanying updates to the "CSS reference syntax" [section](https://developer.mozilla.org/en-US/docs/MDN/Writing_guidelines/Page_structures/Syntax_sections#css_reference_syntax) on the "Syntax sections" page.

### Do you have any supporting links, references, or citations?

_No response_

### Do you have anything more you want to share?

This blocks #26775.

Start with the CSS feature reference page and CSS reference syntax section linked in the issue, then compare existing CSS data type pages to identify their common structure and differences. Done means both guideline sections describe a consistent template and organization for Syntax, Values, Formal syntax, Description, and Interpolation.

Written by the indexing model from the issue text.